Portable Sound Systems

Portable sound systems range from self-contained to very complex. This article covers two types of simple portable systems - a totally self-contained mini system and a typical powered mixer system. Plus, we've included a list of considerations and a block diagram to help you set up your portable sound system.

Self-Contained Sound System

The simplest type of portable sound system has one or two microphone inputs and a line level (Aux) input with volume and tone controls. The microphone preamp, amplifier and loudspeaker are built into one self-contained unit that can be set on a table or mounted on a stand. This type of system works well for conference room presentations, small banquet room meetings and similar sized events where only one or two microphones are needed. Some systems of this type have a built-in wireless microphone and/or cassette player. The self-contained system is extremely portable and easy to use. It can be battery operated so you don't even need AC power.

Powered Mixer

The next step-up is a powered mixer (see Figure 1). This unit may have six to twelve input channels that are either microphone level or line level (cassette or CD player). They typically have individual channel equalization (usually low, mid and high frequency tone adjustments). Overall output equalization is also available. One or two power amplifiers are built into the powered mixer. These systems require separate loudspeakers to be plugged into the amplifier outputs. The powered mixer is well suited for an outdoor service - when the event requires more power and variety than a self-contained system can provide.

Loudspeakers: Another important element of a powered mixer system is the loudspeakers. Many portable loudspeakers have a 60° by 40° coverage pattern. Sometimes multiple loudspeakers may be needed to cover all the seating area with intelligible sound. (see "Loudspeaker Coverage Patterns" for more information). The loudspeaker enclosure is also very important. This equipment is going to be bumped and banged. Therefore, you want an enclosure that is durable (ie: molded plastic, carpet or fiberglass covered cabinets). Some other considerations are: The size and weight of the loudspeakers. How will they be transported? Who is going to carry the loudspeakers from the van? Your answers should be a factor in your purchasing or rental decisions.

List of Considerations Microphones: How many microphones do you need for your application? What types: vocal, instrument or podium? Mixer/Amp: How many input channels do you need? How many watts of power are needed? Usually 100 - 200 watts are adequate. Loudspeakers: What type of area do you need to cover? Will the event be inside or outside? If inside, is the seating area long and narrow? Or is the seating wide and fan shaped? Is there a balcony and under balcony? Do you need monitor loudspeakers? Knowing the coverage patterns of the loudspeaker will help you decide how many are needed for good coverage and intelligibility. Knowing these answers will help you provide good sound to the whole audience. Cables: How many microphone cables, line level cables and loudspeaker cables will be needed? Spares are always helpful in case of an emergency. Don't forget the Gaffer's tape to tape down cables for neatness and safety. Stands: How many microphone and loudspeaker stands will you need? Remember, there are different stand styles and accessories such as booms, goosenecks, etc. Direct Box: How many will be needed? One direct box is needed for each electronic instrument. The direct box converts the line level output of the electronic instrument to microphone level. NOTE: You need a microphone and an instrument cable for each direct box you use. Audio Snake: How far from the platform will the sound operator set-up the mixer?

Location of operator: Another aspect to think about is where the mixer is going to be operated - the platform or another location. If the sound will be operated from a distance, such as from the rear of an auditorium, it will be desirable to use an audio "snake" for the microphones. The snake is a single cable that has multiple conductors. Instead of running many microphone cables, you can lay out one snake cable. There are even snakes with loudspeaker cables included. They are often called power snakes.

Transportation: As stated earlier, any portable equipment is going to be bumped and banged. It is a good idea to have some kind of protection for the equipment. Some systems come with vinyl covers but others need to be purchased separately. A better protection method is to use "road cases" for the equipment. These cases are generally constructed out of laminated plywood or molded plastic. They can be sized to fit the equipment you have.

Applications

What is the type of group or event? What needs will the system have to meet? Here are several examples:

• A typical small ensemble with an electronic keyboard and a guitar for accompaniment will need a handheld vocal microphone for each of the singers with a microphone stand. A direct box will be required for the keyboard, and one for the guitar.
• An ensemble with an accompaniment trax will also need a cassette or CD player.
• A choir requires high quality condenser instrument microphones. The number of microphones depends on the size of the choir. A good rule of thumb is to employ one high quality condenser microphone for about 25 people. A choir of up to 50 would use two microphones. Always remember - in audio, less is better.

Summary

The answers to the questions posed throughout this article along with the "List of Considerations" and the block diagram will help you plan and set up your portable sound system.

For any of your sound system needs, please call us - we're here to help!

by Tracy Paulson © 1996 Internet Sound Institute (www.soundinstitute.com). This articles is for personal use only. Any commercial reproduction is not permitted without permission. To obtain permission, contact ISI at hopi@soundinstitute.com

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